1. Field of the Invention
The invention relates to a metal thermal interface material, and more particularly to a hollowed-out metal thermal interface material. The invention also relates to a thermal module or a packaged microelectronic component that comprises the hollowed-out metal thermal interface material.
2. Description of the Related Art
Packaged microelectronic components, such as high-luminance light emitting diodes, high power insulated gate bipolar transistors, or central processing units, have been developed to have high power, high response rate, and small volume, resulting in devices with highly non-uniform and massive heat flux. The non-uniform and massive heat must be removed to reduce the operating temperature to be lower than the maximum junction temperature, otherwise the components may be damaged or their performance may be deteriorated. In order to enhance the heat being delivered to ambient atmosphere, it is necessary to apply thermal interface materials (TIMs) in the microelectronic components through heat dissipation elements to achieve low and stable interface thermal resistance.
Among various thermal interface materials (TIMs), thermal greases made of macromolecular compound and phase change materials made of low melting-point alloys (LMAs) are the two kinds of TIMs that are highly desirable in use. However, thermal greases are unsatisfactory for high heat-flux-generating microelectronic components. The main reason is that they are quickly degraded or dried out after being used. They also can be pumped out under cyclic thermal stressing when microelectronic components are cyclically powered on and off. On the other hand, LMAs are usually several times of the thermal conductivity of thermal greases. Therefore, the TIMs made of LMAs perform much better in reducing interface thermal resistance than thermal greases do.
Metal TIMs made of LMAs have a phase change property from a solid state to a cream-like state. And, this phase change is activated at the temperature around the operation temperature of microelectronic component. Thus, when the microelectronic component operates, the applied metal TIMs partially or fully melt to fill out the microscopic irregular cavities between the mutual contact surfaces, which facilitates heat transfers across the interface. In general, Metal TIMs operate by absorbing or releasing heat to melt or solidify according to the temperature fluctuation at contact interface. However, when metal TIMs melt, they may overflow out of the mutual contact surfaces that can lead to many undesired effects, especially such as short circuit of microelectronic components.
To prevent the overflowing of metal TIM's melt, many prior arts have been developed. One is to design metal TIMs with a specific structure. For example, a multi-layer metal TIM has a specific structure with at least one phase-change LMA layer bonded to a based metal foil. However, the multi-layer metal TIMs usually perform worse than conventional single-layer metal TIMs. This is because that the multi-layer metal TIMs have additional heat-conducting interfaces, and their thickness is difficult to be reduced. Another prior art to prevent the melt overflowing is to use a gasket to confine the melt in a specific interface area. However, success to avoid the overflowing by this method is not guaranteed due to possible insufficient enclosing space or uneven clamping pressure or crack of the gasket.
When a metal TIM foil is heated to melt, the melt will flow due to applied clamping pressure to fill the interstices between mutual contact surfaces. The redundant melt may move out of the mutual contact surfaces and accumulate to form many beads surround the contact surfaces. The beads accumulated from redundant melt are apt to escape and cause damage of microelectronic components. As the thickness of metal TIMs increases so does the amount of the redundant melt increase. Therefore, reducing thickness of metal TIMs, for example to smaller than 30 μm, is helpful to reduce the redundant melt and thus avoiding overflowing of the TIM melt. However, the optimum thickness of metal TIMs may depend on what the situations and the conditions in where they are applied, such as surface roughness, flatness and operation temperature, etc. For example, a thin metal TIM may be adequate for the interface between IC heat spreader lid and heat sink due to its low contact thermal resistance, only if the surface flatness of the thermal contact surfaces is not very poor. Another example, a thick metal TIM may be good for the interface between the IC die and its heat spreader lid. Because this is not only can reduce the interface thermal resistance, but also can accommodate the thermal stress between the IC die and its heat spreader lid.
Thus, it is necessary to develop a thermal interface material with a novel structure and an appropriate thickness to avoid overflowing of the melt of the thermal interface material. Besides, by introducing such novel interface materials into packaged microelectronic components, not only the performance of the components can be improved, but also the damage issues associating with overflowing of melt can be avoided.